In the manufacture of printed circuits, namely printed circuit boards or copper clad laminates, sheets of copper foil are typically bonded to a dielectric layer of a partially cured epoxy resin impregnated with woven glass fiber (conventionally referred to as a "pre-preg") as in the case of a circuit board, or onto another layer or foil as in the case of a copper clad laminate.
The copper foil used in forming printed circuit boards is typically produced by an electrodeposition process that forms a generally continuous strip of copper. This strip is ultimately cut into sheets that are used to form copper clad laminates. Printed circuit manufacturers use the laminates to produce printed circuit boards. A particular problem associated with the formation of printed circuit boards and copper clad laminates is contamination of the foil sheet. In this respect, any foreign matter, such as resin dust, fiberglass fibers, hair, grease, oil or the like, may result in dots, dents, deposits or pits on the copper foil that can adversely affect the later formation of the conductive paths forming the printed circuits.
Contamination of the copper foil may occur at any of the different processing steps the foil undergoes from its initial formation to its use in forming printed circuits. For example, contamination may occur following the manufacturing of the copper foil, particularly during the steps in preparing the copper foil for shipping and during the manufacturing steps in preparing and bonding the copper foil to a substrate or to another foil sheet. Cutting the foil strip into sheets may result in small metal slivers or shavings on the foil. Further, other machinery and materials used in moving the foil may be a source of other types of contamination, such as dust, grease or oil droplets, that may fall onto the surface of the foil and become embedded therein as the foil passes over rollers and other surfaces.
To protect the copper foil during subsequent handling and shipping, it has been known to secure a metal substrate to one side of a copper foil to protect the same. However, each of the foregoing steps in protecting and insuring against contamination of the foil is costly and time-consuming.
The present invention overcomes the need to ship and protect the copper foil by forming printed circuits on a polyimide film. The circuits are generated by a continuous process. Multi-layer laminates are made by securing like films having printed circuits thereon.